Electrical musical instrument



Dec. 17, 1940. s. w. DEMUTH 2,225,299

ELECTRICAL MUSICAL INSTRUMENT Filed Oct. 26, 1938 lnnentor Galan Vl/IlJemuth dnorneg Patented Dec. 17, 1940 UNITED STATES 2,225,299 ELECTRICAL MUSICAL INSTRUMENT Galan W.'Demuth, Westville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 26, 1938, Serial No. 237,002

8 Claims. (Cl. 179109) This invention relates to electrical musical instruments and more particularly to the voicing or adjustment of the relative volume of sound from the several strings of such an instrument having electromagnetic pick-ups.

The invention is applicable to pianos and other types of steel string instruments wherein electrical pick-up is desired. In electric pianos, it

has heretofore been customary to adjust the rela- I In the practice of my invention, the pick-ups are mounted at a substantially uniform distance from the strings and the output volume for each note is regulated or adjusted by individually magnetizing the strings corresponding to each note to an appropriate degree and to an appropriate polarity adjacent to the pick-up, thereby either increasing or decreasing the pick-up volume as Another object of the invention is to provide an improved practice for adjusting the volume in such an instrument.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and inspection of the accompanying drawing, in which the single figure shows an edgewise view, partly in section of a bank of strings in a piano with the electromagnetic pick-up and the adjusting device in operative relation thereto.

Referring to the single figure of drawing, a steel string I is represented as a piano string and which may be considered to be the string nearest to the observer of a group of strings in a plane perpendicular to the paper. The steel used for such strings is very readily magnetizable.

The string l0 passes over the usual bridge II and has one end attached to the hitch pin l2 in the pin rail I3, the other end thereof being provided with appropriate tensioning means. Underneath the string a magnetic pick-up is provided consisting of a coil l4 wound on a soft iron core, a permanent magnet l5 of appropriate material, and a soft iron or cold rolled steel strip I6 connecting the magnet l5 and the core of the coil l4. The construction of a preferred form in this pick-up is further described and claimed in my application Serial No. 232,526, filed September 30, 1938, RCV D-6349'.

The series of similar pick-ups, one pick-up for each note, are supported upon the members l1 and I8 running along the length of the group of pick-ups.

The permanent magnet l5 induces magnetism IS in the core of the coil l4, and in the end of the core adjacent the string being of opposite polarity to the end of the magnet adjacent the string I, this being indicated in the drawing by the letters N and S adjacent the coil l4 and the magnet [5 respectively. When the string I0 is sounded, it vibrates in relation to the pick-up coil l4 and thereby induces a current through the coil. The amount of this current depends not only upon the amplitude of vibration of the string ill but also upon the magnetization thereof adjacent to the pick-up pole N. If the magnet I5 is quite strong, this magnetization may be relatively great, while, if the magnet I5 is not so strong, the magnetization of the string will be correspondingly weaker.

I have discovered that the string I0 may permanently magnetize longitudinally in such manner as to compensate for variations in the magnet l5 or variations in the spacings of the pick-up from the strings. In order to accomplish such magnetization, I preferably use a magnet indicated at I9 having poles 20 and 2! spaced apart approximately the same distance as the spacing of the pick-up coil l4 and magnet l5, and of course having opposite polarities as indicated by the letters N and S. This magnet, if desired, may be provided with a handle 22. If the magnet is placed in relation to the string shown in the figure, with its south pole adjacent to the north pole of the pick-up and with its north pole adjacent to the south pole of the magnet 40 and is moved along the string substantially in contact therewith, the string will be permanently magnetized longitudinally. The effectiveness of this magnetization on the pick-up volume depends on how closely the poles of the magnet approach those of the pick-up, or, in other words, when the degree of magnetization in the string adjacent the poles of the pick-up is increased, such magnetization as that above described will materially increase the amplitude of the electrical 50 impulses produced in the coil It for a given amplitude of vibration of the string. If the poles of the magnet l9 are reversed in position relative to the poles of the pick-up unit and the string is magnetized, then the amplitude of the current and the pick-up. coil Hi will be decreased.

By following the above procedure and increasing the output from the pick-ups along the notes which are insufficiently loud or not as loud as the average notes, and by decreasing the amount of pick-up from the notes which are too loud, or which are louder than the average of the notes, the output from all the notes of the instrument have a given amplitude of vibration of the string,

or a given amount of force applied to the keys may be rendered uniform without any mechanical adjustment out of the pick-up coil or the pick-up magnet in relation to the string.

Having now described my invention, I claim:

1. An electrical musical instrument having electromagnetic pick-ups for each note, magnetizable strings in operative relation with said pick-ups, each of said strings 'being permanently magnetized to such a degree as to render the output from said pick-ups uniform for a given degree of excitation of the strings.

2. An electrical musical ins ent including a plurality of electromagnetic pick-ups, magnetizable strings in operative relation with said pickups, each of said strings being permanently magnetized to such a degree as to render the output from said pick-ups uniform for a given degree of excitation of the strings.

3. In the adjustment of the output, from a plurality of electromagnetic pick-ups cooperatively associated with vibratable members of magnetic material, the method which includes selectively permanently magnetizing said vibratable members to such a degree as to render the output from said pick-ups uniform for a given degree of excitation of the strings.

4. In a musical instrument including a plurality of electromagnetic pick-ups cooperatively associated with vibratable members of magnetic materials, the voicing method which includes selectively imparting permanent magnetic poles to predetermined sections of said members.

5. In the adjustment of the output, from a plurality of electromagnetic pick-ups coop ratively associated with vibratable members of magnetic material, the method which includes selectively permanently magnetizing said vibratable members independent of the magnetization induced by said pick-up.

6. In a musical instrument including a plurality of electromagnetic pick-ups cooperatively associated with vibratable members of magnetic materials, the voicing method which includes selectively imparting permanent magnetic poles to predetermined sections or said members independent of the magnetization induced by said pick-up.

7. An electrical musical instrument having electromagnetic pick-ups for each note, magnetizable strings in operative relation with said pick-ups, at least some of said strings being permanently magnetized to such a degree as to render the output from said pick-ups uniform for a given degree of excitation of the strings.

8. An electrical musical instrument including a plurality of electromagnetic pick-ups, magne- -tizable strings in operative relation with said GALAN W. DEMUTH. 

